The present invention is related to a technique for drawing an image on a label surface side of an optical disk.
In the case that drawing operations are carried out with respect to optical disks, methods for drawing the optical disks by performing focus servo controls have been known. However, the drawing operation may become unstable in a certain case that a stable servo system cannot be established due to fluctuations in reflectance factors of respective optical disks, characteristic fluctuations in actuators, fluctuations in laser light amounts, temperature changes, and the like. Under such a circumstance, the following technical ideas have been developed (refer to, for example, JP-A-2002-203321 and JP-A-2005-228382): That is, a focus servo gain control is carried out just after an optical disk is inserted, so that the servo system is adjusted to optimum condition based upon reflection light of laser light irradiated on to the optical disk; and after drawing operations are commenced, the focus servo control is carried out based upon the above-described adjustment.
On the other hand, as to the optical disk on which the drawing operation has been once carried out, reflectance factors of a portion on the optical disk where the drawing operation has been performed are changed, but there are some possibilities that additional drawing operations are wanted to be carried out. In this case, in order to perform the focus gain control which is required before the additional drawing operation is carried out, the irradiation of the laser light for the focus gain control must be performed in an area of the optical disk in which the reflectance factors are slightly changed. As a consequence, it is necessary to judge whether a position of the optical disk where the laser light is to be irradiated corresponds to a recorded area, or an unrecorded area. Generally speaking, in the case of such an optical disk on which data has been recorded, since it is possible to judge whether a position of the optical disk on which laser light is to be irradiated corresponds to a data-recorded area, or a data-unrecorded area, a focus servo gain can be controlled by judging the data-unrecorded area.
On the other hand, in the case of such an optical disk where an image has been drawn, an area of the drawn image includes a plenty of portions where lines have been written and a plenty of portions where lines have not been written. As a result, when a label surface of the optical disk where the image has been drawn is scanned, the portions which are not physically written and the portions where the lines have been written are alternately and frequently switched. As a result, the focus servo gain cannot be controlled in a correct manner.